There are fundamental gaps in knowledge of how interactions essential for erythrocyte invasion by Plasmodium parasites are mediated and how antibodies that target these interactions prevent parasite entry. These gaps hinder our ability to design effective interventions for the global health problem malaria. The long- term goal is to determine how receptor-ligand interactions are mediated at the molecular level and how they can be exploited for preventative, therapeutic and diagnostic purposes. The objectives of this application are to understand the molecular basis of receptor recognition by critical parasite ligands and to establish the mode of inhibition of neutralizing monoclonal antibodies that target these proteins. The central hypothesis of the application is that the binding domains of parasite ligands are conserved yet create distinct receptor-binding pockets to recognize diverse receptors, and that inhibitory antibodies target binding pockets, preventing their formation or accessibility. The rationale for the proposed research is that, once identified, functional regions of parasite ligands can be exploited for novel protein-based interventions and vaccines by focusing the immune response to target functional regions exclusively. Supported by prior published work and strong preliminary data, this hypothesis will be tested by pursuing two specific aims: 1) define the determinants for receptor specificity and selectivity of parasite ligands; and 2) determine the structural basis and mechanism for antibody-mediated inhibition of invasion. Under the first aim, structural, functional and mechanistic studies will be used to comprehensively determine the molecular details of receptor-ligand interactions. Under the second aim, structural and interaction mapping studies will reveal epitopes of parasite ligands targeted by neutralizing antibodies towards identifying epitopes that have the greatest neutralizing potential. The approach is innovative as it will reveal the first structural informatin for a key family of parasite ligands. Innovative protein production systems that exploit human cells lines have been established to produce correctly post- translationally modified receptors as these modifications are critical for receptor-recognition. An innovative approach for antibody epitope discovery has been developed that increases the number of antibodies that can be studied at a given time, including antibodies refractory to crystallization. The proposed research is significant because it is expected to advance and expand our knowledge of receptor-ligand interactions, antibody-antigen interactions, and microbial pathogenesis. It is anticipated that thi knowledge will aid in the direct development of diagnostics, preventative and therapeutic interventions for malaria.